In electronic devices such as mobile phones, smartphones, and tablet terminals, a shield sheet metal that surrounds components mounted on a substrate (hereinafter referred to as “mounted components”) is mounted on the substrate as measures against noise generated by the mounted components. The shield sheet metal suppresses electromagnetic waves (noise) generated by the mounted components, and is mounted on the substrate by a surface mount technology (SMT).
The shield sheet metal is large in size compared to the mounted components. Therefore, a strong stress tends to be applied to a solder joint portion at which a copper foil formed on the substrate and the shield sheet metal are joined to each other when a drop impact or the like is applied to the electronic device. An excessive stress may cause separation of the copper foil. Separation of the copper foil may lead to a reduction in reliability. Therefore, measures against separation of the copper foil have been requested.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 2003-69168 and    [Document 2] Japanese Laid-open Patent Publication No. 08-130361.